From: Sven Eckelmann <sven@narfation.org>
Date: Sat, 31 Aug 2019 14:13:11 +0200
Subject: Provide gif quantization for giflib >= 5.2

Bug-Debian: https://bugs.debian.org/939031

diff -Naur exact-image-1.0.2.orig/codecs/Makefile exact-image-1.0.2/codecs/Makefile
--- exact-image-1.0.2.orig/codecs/Makefile	2016-06-18 21:49:25.000000000 +0200
+++ exact-image-1.0.2/codecs/Makefile	2020-12-11 15:30:44.374504000 +0100
@@ -21,7 +21,7 @@
 ifeq "$(WITHLIBGIF)" "1"
 LDFLAGS += -lgif
 else
-NOT_SRCS += gif.cc
+NOT_SRCS += gif.cc gif_quantization.c
 endif
 
 ifeq "$(WITHJASPER)" "1"
diff -Naur exact-image-1.0.2.orig/codecs/gif.cc exact-image-1.0.2/codecs/gif.cc
--- exact-image-1.0.2.orig/codecs/gif.cc	2017-07-21 16:19:01.000000000 +0200
+++ exact-image-1.0.2/codecs/gif.cc	2020-12-11 15:34:55.340504000 +0100
@@ -160,6 +160,17 @@
   return true;
 }
 
+extern "C" int
+eiGifQuantizeBuffer(unsigned int Width,
+                    unsigned int Height,
+                    int *ColorMapSize,
+                    GifByteType * RedInput,
+                    GifByteType * GreenInput,
+                    GifByteType * BlueInput,
+                    GifByteType * OutputBuffer,
+                    GifColorType * OutputColorMap);
+
+
 bool GIFCodec::writeImage (std::ostream* stream, Image& image, int quality,
 			   const std::string& compress)
 {
@@ -203,8 +214,7 @@
     *bptr++ = b;
   }
    
-  
-  if (GifQuantizeBuffer(image.w, image.h, &ColorMapSize,
+  if (eiGifQuantizeBuffer(image.w, image.h, &ColorMapSize,
 		     RedBuffer, GreenBuffer, BlueBuffer,
 		     OutputBuffer, OutputColorMap->Colors) == GIF_ERROR) {
     return false;
diff -Naur exact-image-1.0.2.orig/codecs/gif_quantization.c exact-image-1.0.2/codecs/gif_quantization.c
--- exact-image-1.0.2.orig/codecs/gif_quantization.c	1970-01-01 01:00:00.000000000 +0100
+++ exact-image-1.0.2/codecs/gif_quantization.c	2020-12-11 15:30:19.181504000 +0100
@@ -0,0 +1,331 @@
+/*****************************************************************************
+
+ quantize.c - quantize a high resolution image into lower one
+
+ Based on: "Color Image Quantization for frame buffer Display", by
+ Paul Heckbert SIGGRAPH 1982 page 297-307.
+
+ This doesn't really belong in the core library, was undocumented,
+ and was removed in 4.2.  Then it turned out some client apps were
+ actually using it, so it was restored in 5.0.
+
+SPDX-License-Identifier: MIT
+
+******************************************************************************/
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "gif_lib.h"
+
+#define ABS(x)    ((x) > 0 ? (x) : (-(x)))
+
+#define COLOR_ARRAY_SIZE 32768
+#define BITS_PER_PRIM_COLOR 5
+#define MAX_PRIM_COLOR      0x1f
+
+static int SortRGBAxis;
+
+typedef struct QuantizedColorType {
+    GifByteType RGB[3];
+    GifByteType NewColorIndex;
+    long Count;
+    struct QuantizedColorType *Pnext;
+} QuantizedColorType;
+
+typedef struct NewColorMapType {
+    GifByteType RGBMin[3], RGBWidth[3];
+    unsigned int NumEntries; /* # of QuantizedColorType in linked list below */
+    unsigned long Count; /* Total number of pixels in all the entries */
+    QuantizedColorType *QuantizedColors;
+} NewColorMapType;
+
+static int SubdivColorMap(NewColorMapType * NewColorSubdiv,
+                          unsigned int ColorMapSize,
+                          unsigned int *NewColorMapSize);
+static int SortCmpRtn(const void *Entry1, const void *Entry2);
+
+/******************************************************************************
+ Quantize high resolution image into lower one. Input image consists of a
+ 2D array for each of the RGB colors with size Width by Height. There is no
+ Color map for the input. Output is a quantized image with 2D array of
+ indexes into the output color map.
+   Note input image can be 24 bits at the most (8 for red/green/blue) and
+ the output has 256 colors at the most (256 entries in the color map.).
+ ColorMapSize specifies size of color map up to 256 and will be updated to
+ real size before returning.
+   Also non of the parameter are allocated by this routine.
+   This function returns GIF_OK if successful, GIF_ERROR otherwise.
+******************************************************************************/
+int
+eiGifQuantizeBuffer(unsigned int Width,
+               unsigned int Height,
+               int *ColorMapSize,
+               GifByteType * RedInput,
+               GifByteType * GreenInput,
+               GifByteType * BlueInput,
+               GifByteType * OutputBuffer,
+               GifColorType * OutputColorMap) {
+
+    unsigned int Index, NumOfEntries;
+    int i, j, MaxRGBError[3];
+    unsigned int NewColorMapSize;
+    long Red, Green, Blue;
+    NewColorMapType NewColorSubdiv[256];
+    QuantizedColorType *ColorArrayEntries, *QuantizedColor;
+
+    ColorArrayEntries = (QuantizedColorType *)malloc(
+                           sizeof(QuantizedColorType) * COLOR_ARRAY_SIZE);
+    if (ColorArrayEntries == NULL) {
+        return GIF_ERROR;
+    }
+
+    for (i = 0; i < COLOR_ARRAY_SIZE; i++) {
+        ColorArrayEntries[i].RGB[0] = i >> (2 * BITS_PER_PRIM_COLOR);
+        ColorArrayEntries[i].RGB[1] = (i >> BITS_PER_PRIM_COLOR) &
+           MAX_PRIM_COLOR;
+        ColorArrayEntries[i].RGB[2] = i & MAX_PRIM_COLOR;
+        ColorArrayEntries[i].Count = 0;
+    }
+
+    /* Sample the colors and their distribution: */
+    for (i = 0; i < (int)(Width * Height); i++) {
+        Index = ((RedInput[i] >> (8 - BITS_PER_PRIM_COLOR)) <<
+                  (2 * BITS_PER_PRIM_COLOR)) +
+                ((GreenInput[i] >> (8 - BITS_PER_PRIM_COLOR)) <<
+                  BITS_PER_PRIM_COLOR) +
+                (BlueInput[i] >> (8 - BITS_PER_PRIM_COLOR));
+        ColorArrayEntries[Index].Count++;
+    }
+
+    /* Put all the colors in the first entry of the color map, and call the
+     * recursive subdivision process.  */
+    for (i = 0; i < 256; i++) {
+        NewColorSubdiv[i].QuantizedColors = NULL;
+        NewColorSubdiv[i].Count = NewColorSubdiv[i].NumEntries = 0;
+        for (j = 0; j < 3; j++) {
+            NewColorSubdiv[i].RGBMin[j] = 0;
+            NewColorSubdiv[i].RGBWidth[j] = 255;
+        }
+    }
+
+    /* Find the non empty entries in the color table and chain them: */
+    for (i = 0; i < COLOR_ARRAY_SIZE; i++)
+        if (ColorArrayEntries[i].Count > 0)
+            break;
+    QuantizedColor = NewColorSubdiv[0].QuantizedColors = &ColorArrayEntries[i];
+    NumOfEntries = 1;
+    while (++i < COLOR_ARRAY_SIZE)
+        if (ColorArrayEntries[i].Count > 0) {
+            QuantizedColor->Pnext = &ColorArrayEntries[i];
+            QuantizedColor = &ColorArrayEntries[i];
+            NumOfEntries++;
+        }
+    QuantizedColor->Pnext = NULL;
+
+    NewColorSubdiv[0].NumEntries = NumOfEntries; /* Different sampled colors */
+    NewColorSubdiv[0].Count = ((long)Width) * Height; /* Pixels */
+    NewColorMapSize = 1;
+    if (SubdivColorMap(NewColorSubdiv, *ColorMapSize, &NewColorMapSize) !=
+       GIF_OK) {
+        free((char *)ColorArrayEntries);
+        return GIF_ERROR;
+    }
+    if (NewColorMapSize < *ColorMapSize) {
+        /* And clear rest of color map: */
+        for (i = NewColorMapSize; i < *ColorMapSize; i++)
+            OutputColorMap[i].Red = OutputColorMap[i].Green =
+                OutputColorMap[i].Blue = 0;
+    }
+
+    /* Average the colors in each entry to be the color to be used in the
+     * output color map, and plug it into the output color map itself. */
+    for (i = 0; i < NewColorMapSize; i++) {
+        if ((j = NewColorSubdiv[i].NumEntries) > 0) {
+            QuantizedColor = NewColorSubdiv[i].QuantizedColors;
+            Red = Green = Blue = 0;
+            while (QuantizedColor) {
+                QuantizedColor->NewColorIndex = i;
+                Red += QuantizedColor->RGB[0];
+                Green += QuantizedColor->RGB[1];
+                Blue += QuantizedColor->RGB[2];
+                QuantizedColor = QuantizedColor->Pnext;
+            }
+            OutputColorMap[i].Red = (Red << (8 - BITS_PER_PRIM_COLOR)) / j;
+            OutputColorMap[i].Green = (Green << (8 - BITS_PER_PRIM_COLOR)) / j;
+            OutputColorMap[i].Blue = (Blue << (8 - BITS_PER_PRIM_COLOR)) / j;
+        }
+    }
+
+    /* Finally scan the input buffer again and put the mapped index in the
+     * output buffer.  */
+    MaxRGBError[0] = MaxRGBError[1] = MaxRGBError[2] = 0;
+    for (i = 0; i < (int)(Width * Height); i++) {
+        Index = ((RedInput[i] >> (8 - BITS_PER_PRIM_COLOR)) <<
+                 (2 * BITS_PER_PRIM_COLOR)) +
+                ((GreenInput[i] >> (8 - BITS_PER_PRIM_COLOR)) <<
+                 BITS_PER_PRIM_COLOR) +
+                (BlueInput[i] >> (8 - BITS_PER_PRIM_COLOR));
+        Index = ColorArrayEntries[Index].NewColorIndex;
+        OutputBuffer[i] = Index;
+        if (MaxRGBError[0] < ABS(OutputColorMap[Index].Red - RedInput[i]))
+            MaxRGBError[0] = ABS(OutputColorMap[Index].Red - RedInput[i]);
+        if (MaxRGBError[1] < ABS(OutputColorMap[Index].Green - GreenInput[i]))
+            MaxRGBError[1] = ABS(OutputColorMap[Index].Green - GreenInput[i]);
+        if (MaxRGBError[2] < ABS(OutputColorMap[Index].Blue - BlueInput[i]))
+            MaxRGBError[2] = ABS(OutputColorMap[Index].Blue - BlueInput[i]);
+    }
+
+#ifdef DEBUG
+    fprintf(stderr,
+            "Quantization L(0) errors: Red = %d, Green = %d, Blue = %d.\n",
+            MaxRGBError[0], MaxRGBError[1], MaxRGBError[2]);
+#endif /* DEBUG */
+
+    free((char *)ColorArrayEntries);
+
+    *ColorMapSize = NewColorMapSize;
+
+    return GIF_OK;
+}
+
+/******************************************************************************
+ Routine to subdivide the RGB space recursively using median cut in each
+ axes alternatingly until ColorMapSize different cubes exists.
+ The biggest cube in one dimension is subdivide unless it has only one entry.
+ Returns GIF_ERROR if failed, otherwise GIF_OK.
+*******************************************************************************/
+static int
+SubdivColorMap(NewColorMapType * NewColorSubdiv,
+               unsigned int ColorMapSize,
+               unsigned int *NewColorMapSize) {
+
+    unsigned int i, j, Index = 0;
+    QuantizedColorType *QuantizedColor, **SortArray;
+
+    while (ColorMapSize > *NewColorMapSize) {
+        /* Find candidate for subdivision: */
+	long Sum, Count;
+        int MaxSize = -1;
+	unsigned int NumEntries, MinColor, MaxColor;
+        for (i = 0; i < *NewColorMapSize; i++) {
+            for (j = 0; j < 3; j++) {
+                if ((((int)NewColorSubdiv[i].RGBWidth[j]) > MaxSize) &&
+                      (NewColorSubdiv[i].NumEntries > 1)) {
+                    MaxSize = NewColorSubdiv[i].RGBWidth[j];
+                    Index = i;
+                    SortRGBAxis = j;
+                }
+            }
+        }
+
+        if (MaxSize == -1)
+            return GIF_OK;
+
+        /* Split the entry Index into two along the axis SortRGBAxis: */
+
+        /* Sort all elements in that entry along the given axis and split at
+         * the median.  */
+        SortArray = (QuantizedColorType **)malloc(
+                      sizeof(QuantizedColorType *) * 
+                      NewColorSubdiv[Index].NumEntries);
+        if (SortArray == NULL)
+            return GIF_ERROR;
+        for (j = 0, QuantizedColor = NewColorSubdiv[Index].QuantizedColors;
+             j < NewColorSubdiv[Index].NumEntries && QuantizedColor != NULL;
+             j++, QuantizedColor = QuantizedColor->Pnext)
+            SortArray[j] = QuantizedColor;
+
+	/*
+	 * Because qsort isn't stable, this can produce differing 
+	 * results for the order of tuples depending on platform
+	 * details of how qsort() is implemented.
+	 *
+	 * We mitigate this problem by sorting on all three axes rather
+	 * than only the one specied by SortRGBAxis; that way the instability
+	 * can only become an issue if there are multiple color indices
+	 * referring to identical RGB tuples.  Older versions of this 
+	 * sorted on only the one axis.
+	 */
+        qsort(SortArray, NewColorSubdiv[Index].NumEntries,
+              sizeof(QuantizedColorType *), SortCmpRtn);
+
+        /* Relink the sorted list into one: */
+        for (j = 0; j < NewColorSubdiv[Index].NumEntries - 1; j++)
+            SortArray[j]->Pnext = SortArray[j + 1];
+        SortArray[NewColorSubdiv[Index].NumEntries - 1]->Pnext = NULL;
+        NewColorSubdiv[Index].QuantizedColors = QuantizedColor = SortArray[0];
+        free((char *)SortArray);
+
+        /* Now simply add the Counts until we have half of the Count: */
+        Sum = NewColorSubdiv[Index].Count / 2 - QuantizedColor->Count;
+        NumEntries = 1;
+        Count = QuantizedColor->Count;
+        while (QuantizedColor->Pnext != NULL &&
+	       (Sum -= QuantizedColor->Pnext->Count) >= 0 &&
+               QuantizedColor->Pnext->Pnext != NULL) {
+            QuantizedColor = QuantizedColor->Pnext;
+            NumEntries++;
+            Count += QuantizedColor->Count;
+        }
+        /* Save the values of the last color of the first half, and first
+         * of the second half so we can update the Bounding Boxes later.
+         * Also as the colors are quantized and the BBoxes are full 0..255,
+         * they need to be rescaled.
+         */
+        MaxColor = QuantizedColor->RGB[SortRGBAxis]; /* Max. of first half */
+	/* coverity[var_deref_op] */
+        MinColor = QuantizedColor->Pnext->RGB[SortRGBAxis]; /* of second */
+        MaxColor <<= (8 - BITS_PER_PRIM_COLOR);
+        MinColor <<= (8 - BITS_PER_PRIM_COLOR);
+
+        /* Partition right here: */
+        NewColorSubdiv[*NewColorMapSize].QuantizedColors =
+           QuantizedColor->Pnext;
+        QuantizedColor->Pnext = NULL;
+        NewColorSubdiv[*NewColorMapSize].Count = Count;
+        NewColorSubdiv[Index].Count -= Count;
+        NewColorSubdiv[*NewColorMapSize].NumEntries =
+           NewColorSubdiv[Index].NumEntries - NumEntries;
+        NewColorSubdiv[Index].NumEntries = NumEntries;
+        for (j = 0; j < 3; j++) {
+            NewColorSubdiv[*NewColorMapSize].RGBMin[j] =
+               NewColorSubdiv[Index].RGBMin[j];
+            NewColorSubdiv[*NewColorMapSize].RGBWidth[j] =
+               NewColorSubdiv[Index].RGBWidth[j];
+        }
+        NewColorSubdiv[*NewColorMapSize].RGBWidth[SortRGBAxis] =
+           NewColorSubdiv[*NewColorMapSize].RGBMin[SortRGBAxis] +
+           NewColorSubdiv[*NewColorMapSize].RGBWidth[SortRGBAxis] - MinColor;
+        NewColorSubdiv[*NewColorMapSize].RGBMin[SortRGBAxis] = MinColor;
+
+        NewColorSubdiv[Index].RGBWidth[SortRGBAxis] =
+           MaxColor - NewColorSubdiv[Index].RGBMin[SortRGBAxis];
+
+        (*NewColorMapSize)++;
+    }
+
+    return GIF_OK;
+}
+
+/****************************************************************************
+ Routine called by qsort to compare two entries.
+*****************************************************************************/
+
+static int
+SortCmpRtn(const void *Entry1,
+           const void *Entry2) {
+	   QuantizedColorType *entry1 = (*((QuantizedColorType **) Entry1));
+	   QuantizedColorType *entry2 = (*((QuantizedColorType **) Entry2));
+
+	   /* sort on all axes of the color space! */
+	   int hash1 = entry1->RGB[SortRGBAxis] * 256 * 256
+	   			+ entry1->RGB[(SortRGBAxis+1) % 3] * 256
+				+ entry1->RGB[(SortRGBAxis+2) % 3];
+	   int hash2 = entry2->RGB[SortRGBAxis] * 256 * 256
+	   			+ entry2->RGB[(SortRGBAxis+1) % 3] * 256
+				+ entry2->RGB[(SortRGBAxis+2) % 3];
+
+    return hash1 - hash2;
+}
+
+/* end */
